1. Field of the Invention
This invention relates to an automotive heating system which heats by the heat of the engine coolant, and more particularly to an automotive heating system which is provided with a heat accumulator in the engine coolant circuit.
2. Description of the Prior Art
There has been in wide use an automotive heating system in which a heat exchanger (sometimes will be referred to as "the heater core", hereinbelow) is provided in the engine coolant circuit and heat of the engine coolant heated by the engine is transferred to air through the heater core. In such a heating system, heating cannot be effected when the temperature of the engine coolant is low. That is, heating cannot be effected until the engine is started and warmed up.
Recently a heat accumulator comes to be employed in an automotive heating system in order to solve the problem that heating cannot be effected when the engine is cold. That is, the heat accumulator receives heat from the engine coolant and stores it when the temperature of the engine coolant is higher than the temperature of the heat accumulator and gives heat to the engine coolant when the temperature of the coolant is lower than the temperature of the heat accumulator. The engine coolant can be heated by the heat stored in the heat accumulator irrespective of the temperature of the engine. Thus the heat accumulator is provided between the engine and the heater core so that the engine coolant flowing out of the engine passes through the heat accumulator and the heater core in this order.
In the heating system having the heat accumulator, quick heating can be effected even when the engine is cold by heating the engine coolant by the heat accumulator. However if the engine coolant is passed through the heat accumulator when the heat accumulator is colder than the engine coolant, the coolant is robbed of heat by the heat accumulator and gets colder, whereby a longer time is required for heating.
This problem may be overcome by directly introducing the engine coolant into the heater core without passing the heat accumulator when the temperature of the heat accumulator is lower than the temperature of the engine coolant. However this approach is disadvantageous in that since the engine coolant does not pass through the heat accumulator, heat cannot be stored in the heat accumulator whereas it is desired that heat is stored in the heat accumulator as soon as possible when the heat accumulator is cold.
In Japanese Unexamined Patent Publication No. 2(1990)-120119, there is disclosed a heating system in which a first coolant circulating path for feeding the engine coolant to the heater core via a heat accumulator and a second coolant circulating path for feeding the engine coolant directly to the heater core without passing the heat accumulator are provided, and when the temperature of the heat accumulator is lower than that of the engine coolant while quick heating is required, a part of the engine coolant from the engine is caused to flow through the first coolant circulating path and the other part of the engine coolant is caused to flow through the second coolant circulating path, thereby effecting quick heating while storing heat in the heat accumulator.
However also in this heating system, the part of the engine coolant flowing through the heat accumulator flows into the heater core after being robbed of heat by the heat accumulator, which results in deterioration of the heating efficiency.